Michael Phelps insisted his challenge to Conor McGregor for a swim racewas a joke, but on Monday reportedly offered details on how to make the hypothetical a fair fight.

The distance — 100m freestyle, according to media at Phelps’ appearance opening an Under Armour store in Dubai.

“I said it as a joke. If he wants to swim, I don’t care. I’ll race him,” Phelps said, according to The Nationalin the United Arab Emirates. “If we did it in a year, and I trained for a year, or even six months, I could probably go 48 seconds if I had to. I don’t see him breaking a minute. So I could probably beat him with a 50-meter head start.

“I would definitely exercise the option to have a conversation if he wants to swim.”

Phelps said he has not heard back from McGregor since the Aug. 29 tweet.